int led = 13;
int duration = 1000;
void setup() {
    pinMode(led, OUTPUT);
  digitalWrite(led, LOW);
  // put your setup code here, to run once:
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(led, HIGH);
  delay(duration);
  digitalWrite(led, LOW);
  delay(duration);

}
